A Unique and Remarkable Binary Pulsar
Simon Johnston (Research Centre for Theoretical Astrophysics,
University of Sydney, Australia.)
Abstract PSR B1259--63 is one of the most remarkable pulsars ever discovered. It is the only pulsar known to be orbiting a main sequence Be star and forms the `missing link' in the evolutionary scenario of binary stars. Its orbit is highly elliptical and every 3.5 yr it approaches to within 0.5 AU of its companion star. Its pulse profile is unique among pulsars and shows that the opening angle of its emission cone exceeds 180 degrees. Observations made around the time of closest approach of the two stars show changes in the pulsar's dispersion measure, rotation measure and fractional linear polarization on very short timescales. The pulsar is observed to spin-down during the periastron passage. The companion star to the pulsar has been monitored at optical and UV wavelengths. The system is a radio and X-ray transient and has been detected at gamma-ray energies with the high energy emission probably occurring in a shock front formed by the collision of the two stellar winds.